Ultrafine silver powder introduction

Nano silver particles due to its special structure can produce small size effect, quantum size effects, surface effects and macroscopic quantum tunneling, so that have physical and chemical properties which the traditional materials do not have. Nano silver particles occupy a very important position on surface enhanced Raman Spectroscopy, surface enhanced resonance light scattering spectra, molecular biology, supramolecular systems area, it is one of the important materials for basic research. Nano-Silver powder with high surface activity and catalytic properties, it is widely used in catalyst and ultra-low temperature refrigerator thinner. At the same time, because of its unique physical and chemical properties, it also has been widely applied in immunoassay, sensor development, molecular electronics and so on. In addition, add small amount of silver in chemical fiber can improve some performances of chemical fiber products, and make it have strong sterilization capabilities.

Superfine silver powder based on the form can be divided into roughly spherical, wool, branches and flake types, after complexing silver nitrate with ammonia, add dispersant, add hydrazine restored, washing, filtering, drying to obtain it. According to the grain size can be divided into: fine silver powder, average particle size is 10~40um; very fine silver powder, average particle size is 0.5~10µm; superfine silver powder, average particle size is less than 0.5µm, nano silver powder particle size is less than 0.1µm. Superfine silver powder is most widely used material in the electronics industry, as the conductive phase of conductor paste, powder metallurgy and other raw materials.

Ultrafine silver powder's preparation methods mainly have gas phase method, liquid chromatography and solid-phase. Gas phase method have large invested, low energy consumption, low yield; Superfine silver powder produced by solid-phase with larger particle size and wide particle size distribution range; liquid-phase chemical reduction method is the common methods of low cost and small quantities prepare ultra-fine silver powder.

The principle of liquid-phase chemical reduction method prepared ultrafine silver powder is with reducing agents to deposite silver from its salt or complexes aqueous solution or organic systems in powder form. Commonly used reducing agents have formaldehyde, ascorbic acid, glycerol, organic amines, unsaturated alcohols, sodium citrate, hydrazine and hydrazine compounds, commonly used hydrazine hydrate. In silver ammonia solution, adding a certain amount of nitrate additives, under the effect of hydrazine, adjust the amount of additives, can get different size silver powder. The used nitrate additives can be 1 or 2 kinds, the added amount determined according to the requirements, silver powder prepared by this method with small particle size, small particle size distribution and good reproducibility.

The process of using hydrazine hydrate method to prepare pure silver powder from massive silver or silver nitrate solution, from massive silver or silver nitrate solution refined silver powder generally does not use chlorine or sodium-containing agents. Massive silver is first dissolved in dilute nitric acid prepared as pure silver nitrate solution. Pure silver nitrate solution adds ammonia to pH 8-10, slowly added with twice the theoretical amount of aqueous hydrazine at room temperature and stirring, restore for 30 min, stand outputs fine sponge silver. After filtering, washing, drying, sieving will output qualified silver.

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